Gel compositions

ABSTRACT

The invention relates to a composition which comprises a dispersion of micro spheres in a gel comprising an oily base and an organic polymeric gelling agent.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of priority International ApplicationNo. PCT/GB01/01428, filed Mar. 29, 2001 and published in English asInternational Publication No. WO 01/74480 A1 on Oct. 11 2001 whichclaims priority and from GB 0007827.9, filed Mar. 31, 2000. The entiredisclosure of both priority documents is incorporated herein byreference.

BACKGROUND OF THE INVENTION

Communications cables typically comprise a signal-conducting coresurrounded by a protective sheath. The core can, for example, conductlight signals or electrical signals. In many cables the space betweenthe conductor and sheath contains a filler, the role of which is toprotect and cushion the core from external forces that might be producedby, for example, bending or coiling, particularly in the case offibre-optic cables. A further role of the filler is the prevention ofwater ingress which is particularly pertinent should the core comprise ametal such as copper. In order to fulfil these requirements, the fillermust display a number of characteristics. The filler must be ofsufficient viscosity in order to allow lateral movement of the corewhich occurs during, for example, bending, coiling or laying. Theviscosity must however not be so low as to allow a drip wise loss offiller during vertical laying of cables. Moreover, this balance ofproperties must be maintained over a temperature range of −40 to +80° C.The filler must be formulated to be chemically compatible with cablegrade polymers, which includes not only the cable sheath but alsocoatings typically found on optical fibres. The filler should also showa high degree of elasticity in order to absorb the force of impacts thatthe cable sheath may undergo during its operating lifetime. Relativelyhigh ambient temperatures can be reached through fabrication of suchcables resulting in thermal expansion of the filler which then leads tothe formation of holes and cavities on cooling. Such holes and cavitiescan potentially become a water path which in fibre optic cables can leadto attenuation of the light wave guide. Thus cable fillers shouldideally show low thermal conductivity. For electrical applications orcores transmitting electrical signals, it is advantageous if the fillerhas a low permitivity thus insulating the conducting core. This has theadditional benefit of rendering the filler hydrophobic therebyprotecting the core from water ingress. The anti-drip resistance offillers can be improved by reducing their specific weight. Finally, foreasy handling, it is preferred if the filler is semi-dry to the touch,rather than sticky.

Existing fillers used in telecommunication cables include oil gels whichare primarily blends of oils and gelling agents. In application, theypenetrate between bundles of for example, densely packed insulatedcopper conductors and in so doing insulate them from moisture. The oil,which comprises a major part of the blend, can be a naphthenic orparaffinic processing oil, a mineral oil, a synthetic product such as apolybutane or a silicone oil. Gelling agents include waxes, silicic(silica gels) acids, fumed silica, fatty acid soaps and thermoplasticelastomers. Typically the gelling agent comprises less than 10% of thewhole.

One particular family of thermoplastic elastomers marketed under thetrade mark ‘Kraton’ (Shell Chemical Company), comprises di-block,tri-block or multi-atm molecular configurations of rubber andpolystyrene segments.

U.S. Pat. No. 5,657,410 describes an optical transmission element whichincludes a filler comprising between 80% and 95% by weight of amonomeric plasticizer having a molecular weight in the range 200-2000grams per mole. Such monomeric plasticizers include esters ofphthalates, trimellitates, phosphates and fatty esters. Additionalsubstances may also be added such as thickeners. The thickener can takethe form of small spheres. Hollow spheres are preferred due to theirgreat compressibility and easy processibility. Thixotropic agents mayalso advantageously be added. They include finely divided or fumedsilica, alumina, and bentonites as well as mixtures of these substances.

The use of micro spheres, e.g. hollow micro spheres, in cable fillingcompounds is also described in U.S. Pat. No. 5,698,615. In thisdisclosure the cable filler comprises a substantially dry hydrophiliccomposition containing inter alia, in addition to the micro spheres,water absorbent swellable powder particles, preferably of particle sizerange 1-30 μm and a “parting powder” having particles of preferably1/100th the size of the swellable powder particles. Due to thehydrophilic nature of the swellable powder particles, the compositionalways retains some water. The parting powder particles are disposedbetween the swellable powder particles to prevent agglomeration as theswellable polymer particles absorb water. Suitable swellable powderparticles are those based on the polyacrylic acid sodium salt. Theparting powder particles are typically inorganic powders such as talcum,mica, graphite and silicates. The absorption of water by the swellablepowder particles transforms the dry composition into a gel which sealsthe core from further water ingress. The compositions can also contain asmall amount of an oil or an adhesive to reduce any potential dusthazard.

WO 99/15582 discloses a composition which includes expandable hollowmicro spheres for use in encapsulation of for example semi-conductorchips. Such hollow micro spheres, similar in morphology to the microspheres disclosed in U.S. Pat. No. 5,657,410 and U.S. Pat. No.5,698,615, comprise a polymeric shell encapsulating a blowing agent.When heated, the polymeric shell of the expandable micro spheresgradually softens and the liquid blowing agent, typically isobutane,starts to evaporate thus expanding the microsphere.

A light wave guide lead is disclosed in U.S. Pat. No. 5,335,302 whichcomprises at least one light wave guide accommodated in a protectivesheath and embedded in a pasty filling material containing small microspheres. The small micro spheres, which can be solid and rigid, solidand elastic or hollow and elastic, are included as fillers to reduce thecost, and to provide improved rheological and cushioning properties. Apreferred filler comprises an oil, a thixotropic agent (for examplefumed silica) and an unspecified organic thickener.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a composition,particularly a composition suitable for use as a cable filler, whichcomprises a dispersion of micro spheres in a gel comprising an oily baseand an organic polymeric gelling agent.

In another aspect, the invention provides a composition, particularly acomposition suitable for use as a cable filler, which comprises adispersion of micro spheres in a gel comprising an oily base and anorganic polymeric gelling agent, the composition containingsubstantially no thixotropic agent other than the organic polymericgelling agent.

In a further aspect, the invention provides a composition, particularlya composition suitable for use as a cable filler, which comprises adispersion of micro spheres in a gel comprising an oily base and apolymeric gelling agent wherein the polymeric gelling agent comprises,consists essentially of, or consists of a thermoplastic elastomer.

Another aspect of the invention provides a composition, particularly acomposition suitable for use as a cable filler, which comprises adispersion of micro spheres in a gel comprising an oily base and apolymeric gelling agent wherein the polymeric gelling agent comprises,consists essentially of, or consists of a thermoplastic elastomer otherthan polystyrene-isoprene rubber.

Yet another aspect of the invention provides a composition, particularlya composition suitable for use as a cable filler, which comprises adispersion of micro spheres in a gel comprising an oily base and apolymeric gelling agent wherein the polymeric gelling agent comprises,consists essentially of, or consists of a thermoplastic elastomer,excluding compositions containing polystyrene-isoprene rubber and anorganic thickener.

A further aspect of the invention provides a composition, particularly acomposition suitable for use as a cable filler, which comprises adispersion of micro spheres in a gel comprising an oily base and athermoplastic elastomer as a gelling agent, the composition containingsubstantially no thixotropic agent in addition to the thermoplasticelastomer.

Another aspect of the present invention is a gel composition comprisinga dispersion of organic microspheres in a gel comprising an oily baseand a thermoplastic elastomer, the gel containing substantially nothixotropic agent in addition to the thermoplastic elastomer and beingsubstantially free from silica, for example fumed silica. In the contextof the gel containing substantially no thixotropic agent in addition tothe thermoplastic elastomer and being substantially free from silica,for example fumed silica. In the context of the present invention, theterm “substantially no thixotropic agent other than the organicpolymeric gelling agent” means that the composition contains less than0.2% of a thixotropic agent other than the organic polymeric gellingagent, and the term “substantially free from silica” means that thecomposition contains less than 0.1% silica.

A particular embodiment of the invention is a composition, particularlya composition suitable for use as a cable filler, which comprises adispersion of micro spheres in a gel comprising an oily base and anorganic polymeric gelling agent wherein the gel is substantially free offumed silica.

The gels of the invention may additionally contain an anti-oxidant.

The oily base can comprise a hydrocarbon oil or a silicone oil.Particularly preferred hydrocarbon oils include white mineral oils andpoly(α-olefin) synthetic oils. The oily base typically constitutes 1-99%by weight of the gel, more preferably 5-99% by weight of the gel, inparticular 80-99% by weight of the gel.

Examples of thermoplastic elastomers include thermoplastic rubbers. Thethermoplastic elastomer can be a copolymer, for example a blockcopolymer processing a di-block, a tri-block, or a multi-arm molecularconfiguration. In one particular embodiment, the blocks are comprised ofeither rubber or polystyrene. The rubber can be saturated olefin rubbercomposed of ethylene, propylene or butylenes monomer units.Alternatively, the rubber can be an unsaturated olefin rubber comprisingbutadiene or isoprene monomer units.

Particular examples of thermoplastic elastomers includestyrene-ethylene/butylene styrene tri-block copolymer (SEBS),styrene-ethylene/propylene di-block copolymer (SEP), ethylene/propylenemulti-arm copolymer (EP), styrene-butadiene-styrene tri-block copolymer(SBS) and styrene-isoprene-styrene tri-block copolymer (SIS).

Commercially available thermoplastic elastomers include the copolymersavailable under the trade mark “Kraton” from Shell.

The polymeric gelling agent is typically used in proportions in therange 1-10% by weight of the composition more preferably, in the range2-9% by weight of the composition, in particular in the range 3-8% byweight of the composition.

The micro spheres can be for example, solid rigid micro spheres, solidelastic micro spheres or compressible hollow micro spheres. Solid rigidmicro spheres can be formed from a thermosetting resin such asmelamine-formaldehyde resin which has a relatively low thermal expansioncoefficient and in use would tend to lower the overall expansioncoefficient of the gel. This is particularly advantageous where the gelmay be heated during manufacture of, for example, fibre optic leads.During such processes, conventional materials tend to expand when heatedleaving holes or cavities around the wave guides on cooling. The holesor cavities can, under certain conditions, lead to an increase inattenuation of the light wave guides. The melamine-formaldehyde microspheres, available from Ubitek Company of Uchte, preferably have adiameter of <10 μm, in particular <1 μm.

Examples of solid elastic micro spheres are those comprisingpolyisoprene. The polyisoprene is not only elastic in its own right butcan additionally absorb considerable quantities of the oily base therebybecoming even more elastic. The mean diameter of the micro spheres ispreferably <10 μm, more preferably <1 μm.

One preferred embodiment of the invention uses compressible hollow microspheres each comprising a polymeric shell encapsulating a blowing agent.The polymeric shell is generally formed from a copolymer, for example acopolymer of vinylidene chloride and acrylonitrile. The blowing agentcan, for example, be isobutane or isopentane. In addition, the microspheres can be expanded or unexpanded. The polymeric shell of theunexpanded micro spheres softens on heating, so allowing the evaporatingblowing agent to expand the volume of the micro spheres.

Such hollow micro spheres whether expanded or initially unexpanded,display a high degree of elasticity and additionally have a low specificweight. Use of such micro spheres in the gels disclosed in thisinvention is advantageous in that they lower the overall specific weightof the gels and thus reduce or eliminate drip-out during vertical layingof the cable.

The hollow nature of the micro spheres means that the proportion ofsolid material is very low relative to the volume. Thus their additionto the gels of the invention leads to a reduction in the overall thermalconductivity and a reduced likelihood of decomposition of any of thecomponents of the gel or the creation of voids under the elevatedtemperatures reached during cable manufacture. The superior elasticproperties of the hollow micro spheres over their solid counterpartsgives improved protection to, for example, light wave guides duringconveying, coiling or laying. Additionally, the problem of attenuationof light waveguides due to the presence of holes or cavities within thecable filling is also reduced as any increase in volume of the bulk ofthe filler due to heating during cable manufacture is matched by aconverse reduction in the volume of the hollow micro spheres. Due to thecompressible nature of such hollow micro spheres, their typicaldiameters are greater than those of their solid counterparts. In fibreoptic cable applications, diameters in the range of the diameter of thelight wave guide can be used. For expanded hollow micro spheres, thediameters will typically lie in the range 1-200 μm, more usually lessthan 100 μm, typically less than 75 μm, for example 15 to 55 μm. Forunexpanded hollow micro spheres, the mean diameter prior to expansion istypically in the range up to 50 μm, more usually less than 30 μm, forexample in the range 10 to 20 μm.

The volume proportion of the micro spheres generally differs for solidand hollow counterparts. The solid micro spheres are typically employedin the volume range 1-50% by volume of the gel (v/v), more preferably inthe range 5-50% v/v. Where hollow micro spheres are used, they aretypically present in the range 1-95% v/v, more preferably 5-95% v/v, inparticular 50-95% v/v, the foregoing figures to the expanded volumes.

The anti-oxidant can be selected from those commonly used in the artPhenolic anti-oxidants are preferred. The anti-oxidant is typicallypresent in an amount 0.01-1% w/w, for example 0.1-1% w/w.

In a further aspect, the invention provides a composition ashereinbefore defined for use as a cable filler.

In another aspect, the invention provides a cable, such as acommunications cable, containing a filler as hereinbefore defined.

In a still further aspect, the invention provides a cable comprising aconducting core surrounded by a sheath, a composition as hereinbeforedefined being disposed between the conducting core and the sheath. Theconducting core can be, for example, an electrical conductor or a lightconductor. The electrical conductor can be, for example, a conductor forconducting electrical signals such as telephone signals.

In a further aspect, the invention provides a process for making a cablecomprising a conducting core and a sheath, the process comprising thestep of extruding the cable sheath onto the conducting core andinterposing a composition as hereinbefore defined between the conductingcore and sheath during the extrusion step.

In another aspect, the invention provides a process for preparing a gelas hereinbefore defined; the process comprising:

-   (a) heating the oily base to a temperature in the range 110° C. to    120° C.;-   (b) adding the polymeric gelling agent to the oily base and blending    to form a mixture;-   (c) cooling the mixture to a temperature of less than 90° C.;-   (d) adding and blending in the micro spheres; and optionally-   (e) adding and blending in an anti-oxidant: and/or-   (f) maintaining the mixture under vacuum to remove entrapped gas.

In a preferred embodiment, the process comprises:

-   (i) blending at least one oil in a heating-blending tank;-   (ii) heating the blended oils to 110-120° C. in a stirred    heating-blending tank;-   (iii) adding and blending the polymeric gelling agent to the oily    base under high shear for no more than one hour after of the oily    base to a blending-cooling tank, allowing the temperature of the    blend to rise to more than 120-130° C.;-   (iv) cooling the blend to <90° C. and transferring to a stirred main    reactor,-   (v) adding and blending an antioxidant;-   (vi) adding and blending the micro spheres, drawn to the reactor    under vacuum or pumping, for at least two minutes;-   (vii) maintaining the vacuum for at least another 10 minutes in    order to effect removal of air bubbles prior to release of the    finished gel.

Although the temperature of the mixture is typically <90° C. aftercooling, more preferably it is <80° C., in particular it is <70° C.

Further and particular aspects of the invention are as set out in theclaims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be illustrated, but not limited, by reference tothe particular embodiments shown in the accompanying drawings, in which:

FIG. 1 shows a cross-sectional view of an electrical cable; and

FIG. 2 shows a cross-sectional view of an optical cable;

FIG. 3 is a graph of viscosity against shear rate for the composition ofExample 1 at 25° C.; and

FIG. 4 is a graph of viscosity against shear rate for the composition ofExample 2 at 25° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a cross-sectional view of an electrical cable 11,comprising, in this example, four electrical leads 13 encased incladding 12. The electrical leads 13 themselves comprise an electricalconductor 14, preferably of copper, and an outer insulation 15,typically of polyethylene. Interspersed between the electrical leads 13and the outer cladding 12, is a filler gel composition 16. In thisembodiment, the filler composition can comprise an oily base, athermoplastic rubber as polymeric gelling agent and micro spheresdispersed therein and optionally an anti-oxidant. The electrical cable,typically comprising a copper core, can be used for the purposes oftelecommunications or distribution of electricity.

Although FIG. 1 shows a cross-sectional view of an electrical cablecomprising four conductors in a star quad configuration, it will beappreciated that cables having a variety of different configurations canbe used as alternatives to the configuration shown.

FIG. 2 shows an optical cable 21 comprising three optical fibre buffertubes 23 encased in cladding 22. The optical fibre buffer tubes 23themselves consist of an optical fibre 24 provided with a protectivecoating 26 and a protective sheath 25. The filler composition 27 isdisposed between the coated optical fibre and the protective sheath.Additionally, it fills the interstices formed between individual buffertubes and between the buffer tubes and the internal surface of the cablecladding.

Examples of specific gels suitable for use in cables, such as the cablesillustrated in FIGS. 1 and 2 are as follows:

EXAMPLE 1

A gel filler was prepared having the following composition:

Component Concentration (% wt.) White mineral oil 89.0 SN 500 (Mobil)Thermoplastic elastomer 5.5 Kraton 1701 or 1702 (Shell) Micro spheres(pre-expanded) 5.0 Expancel 091 DE (Triones Chems. Int.) Anti-oxidant0.5 Irganox L 135 (Ciba-Geigy)

The gel filler of this example is suitable for filling the intersticesbetween the tubes and conductors (flooding) and is not in direct contactwith the fibre guides.

The gel was prepared as follows:

The oily base was introduced into a stirred heating-blending tank andheated to 110-120° C. before transferring to a high shearblending-cooling tank, whereupon the thermoplastic elastomer (Kraton)(in the form of granules) was added. The mixture was blended under highshear conditions using a multi-purpose immersion type mixer emulsifier(Silverson Machines Limited, Model GDD 25) for no more than 60 minutes.During the blending process, the temperature of the mixture was allowedto rise to 120-130° C. The mixture was cooled by means of a cold waterchiller system, and the chilled mixture was transferred to a stirredmain reactor where the anti-oxidant was added. A vacuum was then createdinside the reactor in order to suck in the micro spheres which weremixed into the blend over a period of at least two minutes. The vacuumwas maintained for at least a further ten minutes in order to effectremoval of any air bubbles. The vacuum was then released, the stirrerswitched off and samples taken prior to release of the finished gel fromthe main reactor.

The product was characterised by a number of tests, the results of whichare summarised in Table 1 below. The thermal conductivities referred toin the table were determined as follows:

Specimen discs were created by scooping the gels into a pair of nylonrings of mean internal diameter 70.1 mm and mean thickness 10.03 mm andplacing cling film above and below. A small correction was made to allowfor the extra interface introduced by the cling film. The thermalconductivity of the specimens was measured using a 76 mm guardedhotplate. A pair of specimen discs were mounted, under the pressure oftwo cooled plates, on either side of a guarded heater plate. The cooledplates were maintained at a constant temperature to better than ±0.05°C. The surfaces of the plates had emittances of better than 0.9. Thetemperature of the annular guard on the heater plate was matched to thatof the central part to better than ±0.01° C. in order to minimiselateral heat flow in the specimens. The heater plate and the specimenswere insulated with a glass fibre blanket to further reduce edge heatlosses. The temperature drop through the specimens was fixed at 14° C.and about 5 hours was allowed for thermal equilibrium to be establishedbefore final readings were taken.

The aging test was derived from YD/T839.4-1996 (PRC Method) except thatthe temperature and duration of the test was altered.

TABLE 1 Physical Properties Property Value Test Method Density (20° C.)g/ml 0.356 ASTM D 1475 Viscosity (100 s^(.1), 25° C.) Pa · s 23.63 HaakeVT500 Tube drainage (7 mm id/80° C./24 hrs.) Pass EIA/TIA-455-81A ConePenetration (23° C.) dmm 335 ASTM D937 Cone Penetration (−30° C.) dmm167 ASTM D937 Cone Penetration (−40° C.) dmm 120 ASTM D937 Oilseparation (80° C./24 hrs.) % wt. 0 FTM791 (321) Volatile loss (80°C./24 hrs.) % w/w 0.17 FTM791 (321) OIT (190° C.) min. 34.75 ASTM D3895Thermal conductivity (23° C.) W/m · K 0.077 see above Thermalconductivity (80° C.) W/m · K 0.078 see above Hydrogen generation (80°C./24 hrs.) μl/g 0.010 Acid Value mgKOH/g 0.036 BS2000 Aging (100°C./240 hrs.) Pass see above UV exposure (25° C./14 days) PassTemperature exposure (240° C./5 mins.) Pass OIT ≡ Oxidative inductiontime

Table 1 shows that the density of the gel is low which contributed togood anti-drip properties (measured at 80° C.). Low temperatureperformance was assessed by cone penetration at −40° C. whilst hightemperature performance was tested by a combination of the drip test,oil separation and volatile loss tests all carried out at 80° C. and theoxidative induction time test carried out at 190° C. An oxidativeinduction time in excess of 20 minutes is desirable. The resultsindicate that the gel has a working temperature range of −40 to +80° C.Furthermore the rheological behaviour of the gel, shown in FIG. 3, isthixotropic (shear thinning) allowing for cold pumping and processing,and thus cable filling in the absence of voids created by gel shrinkage.

Thermal conductivity was determined at 23° C. and 80° C. The values forthe conductivity were low reflecting the low density of the gel, andvaried little with temperature suggesting a material possessing adisordered structure. The good insulating properties indicated amaterial possessing good resistance to thermal decomposition that canoccur at the elevated temperatures reached during cable manufacture. Inaddition, the gel would be less sensitive to the thermal expansion andcontraction that can take place during cable manufacture leading to theformation of voids in the cable filling. For purposes of comparison, thethermal conductivities of a range of materials are given in Table 2.

TABLE 2 Thermal Conductivities of Various Materials Material Thermalconductivity W/m · K Comment Aluminium 200 Very good conductor Water 0.6Olive oil 0.17 Paraffin 0.15 Air 0.024 Very good insulator

The gel showed good aging properties and uv and temperature resistance.There was also low hydrogen gas generation.

EXAMPLE 2

A similar gel filler was prepared in a similar manner to that describedin Example 1 but with a different grade of mineral oil. The gel wassuitable for use in small pair telephone copper cable filling andflooding applications.

The gel was subject to a number of physical tests. The results of thephysical tests were similar to those of the composition of Example 1 andtherefore only the electrical properties are quoted in Table 3.

TABLE 3 Physical Properties Property Value Test Method Dielectricconstant (23° C.) 1.62 ASTM D924 Dielectric dissipation factor (1 MHz)4.4 × 10⁻⁴ ASTM D924 Volume resistivity (23° C.) Ohm · cm 2.8 × 10¹⁵ASTM D257 Break down voltage kV 86The gel is characterised by a low relative permitivity (1.62) and a highvolume resistivity (2.8×10¹⁵ Ohm.cm). For purposes of comparison, therelative permitivities of a number of materials are given in Table 4.

TABLE 4 Relative Permitivities of Various Materials Material Relativepermitivity Air (normal pressure) 1.0005 Paraffin wax 2 Paraffin oil 4.7Glass 5–10 Mica 6 Methyl alcohol 32 Water 81

EXAMPLE 3

A gel suitable for use in filling loose tubes and interstitial fillingbetween ribbons and open slotted cores, was prepared in a similar mannerto that described in example 1. The formula for this gel is set outbelow:

Component Concentration (% wt.) Poly α-olefin oil^(a) 66.37 Durasyn 166(Amoco) White mineral oil 22.13 Whiterex 250 (BP/Mobil Thermoplasticelastomer 7.5 Kraton 1701 or 1702 (Shell) Micro spheres (pre-expanded)3.5 Expancel 091 DE (Triones Chems. Int.) Anti-oxidant 0.5 Irganox L 135(Ciba-Geigy) ^(a)The poly α-olefin oil is also supplied by BP/Mobil asSHF 61

The gel was subject to a number of physical tests. The results of thephysical tests, which were similar to the results of the composition ofExample 1, are shown in Table 5.

In addition the tensile strength and coating strip force of opticalfibres were tested according to the standards FOTP-28 and FOTP-178respectively. The optical fibre was CPC6 manufactured by Siecor. Thetests were carried out after ageing of the fibres in forced air chambersfor 30 days at 85±1° C. whilst immersed in the gel. Measurements werecarried out at 20° C. and 70% relative humidity. The tensile strengthwas measured on thirty 0.5 mm samples from four different groups at arate of elongation of 500±50 mm/min. 50 mm samples were used for thecoating strip force tests using a stripping tool at a speed of 500±50mm/min. Average tensile strength and coating strip force values for acontrol sample were 68.89 N and 3.61 N respectively.

TABLE 5 Physical Properties Property Value Test Method Density (20° C.)g/ml 0.438 ASTM D 1475 Viscosity (200 s^(.1), 25° C.) Pa · s 7.95 HaakeVT500 Tube drainage (7 mm id/80° C./24 hrs.) Pass EIA/TIA-455-81A ConePenetration (23° C.) dmm 396 ASTM D937 Cone Penetration (−40° C.) dmm250 ASTM D937 Oil separation (80° C./24 hrs.) % wt. 0 FTM791 (321)Volatile loss (80° C./24 hrs.) % w/w 0.06 FTM791 (321) OIT (190° C.)min. 31.04 ASTM D3895 Thermal conductivity (23° C.) W/m · K 0.077 seeexample 1 Thermal conductivity (80° C.) W/m · K 0.078 see example 1Hydrogen generation (80° C./24 hrs.) 0.015 μl/g Relative permitivity (50Hz, 25° C.) 1.65 ASTM D150 Volume resistivity (23° C.) Ohm · cm 19 ×10¹⁴ ASTM D257 Tensile strength (20° C./70% RH) N 65.07 FOTP - 28Coating strip force (20° C./70% RH) N 3.88 FOTP - 178 Aging (100° C./240hrs.) Pass see example 1 UV exposure (25° C./14 days) Pass Temperatureexposure (240° C./5 mins.) Pass OIT ≡ Oxidative induction time

The shear sensitive behaviour of the viscosity is illustrated in FIG. 4and shows that the gel is thixotropic or shear thinning. This gelalthough of lower viscosity than the gel of example 1, still passed thedrainage test. The low temperature performance, chard by the conepenetration at −40° C., was exceptional. This is particularly importantas this gel is used in direct contact with optical fibres and mustmaintain flexibility at low temperatures to avoid applying stresses tothe aforementioned fibres or micro bending caused by contractio whichcan lead to an increase in attenuation. The tensile strength and coatingstrip force results suggested that there was no deterioration in themechanical strength of the fibres or degradation in the fibre coatingafter exposure to the gel.

EXAMPLE 4

This gel, formulated for filing loose tubes and interstitial fillingbetween ribbons and open slotted cores particularly for use withpolypropylene cable polymers, was prepared in a similar manner to thatdescribed in example 1. The formula for this gel is set out below:

Component Concentration (% wt.) Silicone oil 94.7 F111/5000 (Ambersil)Fumed silica 1.8 M5 (Cabot) Micro spheres (pre-expanded) 3.0 Expancel091 DE (Triones Chems. Int.) Cross-linking additive 0.5

The resulting gel was subject to a number of physical and chemicaltests, the results of which are summarised in Table 6 below.

The gel was tested for compatibility with polypropylene using thefollowing method:

Six 50 mm long samples of buffer loose tubes were weighed to 0.00001 g.Five of the samples were subsequently immersed in the gel and all sixaged in an air-circulated oven at 80° C. for two weeks. The samples werethen re-weighed.

TABLE 6 Physical Properties Property Value Test Method Density (20° C.)g/ml 0.51 ASTM D 1475 Viscosity (100 s^(.1), 25° C.) Pa · s 32.86 HaakeVT500 Tube drainage (7 mm id/80° C./24 hrs.) Pass EIA/TIA-455-81A ConePenetration (23° C.) dmm 340 ASTM D937 Cone Penetration (−40° C.) dmm280 ASTM D937 Oil separation (80° C./24 hrs.) % wt. 4.97 FTM791 (321)Volatile loss (80° C./24 hrs.) % w/w 0.11 FTM791 (321) OIT (190° C.)min. 33.15 ASTM D3895 Hydrogen generation (80° C./24 hrs.) μl/g 0.012Tensile strength (20° C./70% RH) N 66.00 FOTP - 28 Coating strip force(20° C./70% RH) N 4.10 FOTP - 178 Aging (100° C./240 hrs.) Pass seeexample 1 UV exposure (25° C./14 days) Pass Temperature exposure (240°C./5 mins.) Pass Polypropylene compatibility (80° C./ Pass see above 2wks.) OIT ≡ Oxidative induction time

The results from the low temperature cone penetration, and the oilseparation, volatile loss and oxidative induction time experimentssuggest that the operating range of this gel is −40 to +80° C. Thetensile strength and coating strip force results suggested that therewas no deterioration in the mechanical strength of the fibres ordegradation in the fibre coating after exposure to the gel. The gel wasfound to be compatible with polypropylene as there was no weight gain inthe immersed tube samples after aging.

EXAMPLE 5

This gel, formulated for cable flooding and interstitial fillingapplications and is a swellable water blocking gel, was prepared in asimilar manner to that described in example 1. The formula for this gelis set out below:

Component Concentration (% wt.) White mineral oil 89.5 SN 500 (Mobil)Thermoplastic elastomer 4.0 Kraton 1701 or 1702 (Shell Fumed silica 3.0M5 (Cabot) Micro spheres (unexpanded) 2.5 Expancel 551 DU (TrionesChems. Int.) Anti-oxidant 0.5 Irganox L135 (Ciba-Geigy) Monopropyleneglycol 0.5 PGUSP-IS (Arco Chemical)

The gel was subject to a number of physical tests, the results of whichare summarised in Table 7 below.

TABLE 7 Physical Properties Property Value Test Method Density (20° C.)g/ml 0.87 ASTM D 1475 Viscosity (200s^(.1), 25° C.) Pa.s 7.00 HaakeVT500 Cable drainage (80° C./24 hrs.) Pass EIA/TIA-455-81A ConePenetration (25° C.) dmm 340 ASTM D937 Oil separation (80° C./24 hrs.) %wt. 0 FTM791(321) OIT (190° C.) min. >40 ASTM D3895 Hydrogen generation(80° C./24 hrs) μl/g <0.02 Acid Value mgKOH/g <0.5 BS2000 Tensilestrength (20° C./70% RH) N 66.00 FOTP - 28 Coating strip force (20°C./70% RH) N 4.10 FOTP - 178 OIT = Oxidative induction time

The presence of unexpanded hollow micro spheres in the gel meant thatthe filler increased in volume by 1-10% on heating in the temperaturerange 95-140° C. Such heat can originate from the extrusion head duringmanufacture of, for example, fibre optic cables. The swellable nature ofthe gel can help eliminate voids in the cable created on shrinkage ofthe cable filler and ensure a watertight seal around the core. Theelimination of voids also reduces the likelihood of problems ofattenuation associated with fibre optic cables.

The gel can also be used for filling beneath the metallic laminate whereover-flooding with petroleum jelly type material can prevent scaling ofthe overlap whilst under-flooding may create a water path within thecable and lead to the problems of attenuation described above.

It will readily be apparent that numerous modifications and alterationscan readily be made to the compositions exemplified in the Exampleswithout departing from the principles underlying the invention and allsuch modifications and alterations are intended to be embraced by thisapplication.

1. A cable filling or cable flooding composition comprising a dispersionof hollow expanded microspheres in a gel comprising an oily base and athermoplastic elastomer, wherein the microspheres each have a shellformed of a copolymer of acrylonitrile and methacrylonitrile, saidcopolymer having CAS Registry No. 38742-70-0, wherein said compositionis thixotropic under ambient temperature conditions, and wherein saidcomposition has an operating temperature range of about +80 C to about−40 C.
 2. A composition according to claim 1, the composition beingsubstantially free from silica.
 3. A composition according to claim 2,the composition being substantially free from fumed silica.
 4. Acomposition according to claim 1, wherein the oily base comprises atleast one oil selected from naphthenic processing oil, paraffinicprocessing oil, mineral oil, synthetic oils and silicone oil.
 5. Acomposition according to claim 4, wherein the oily base comprises apoly(α-olefin) synthetic oil.
 6. A composition according to claim 1wherein the oily base is present in an amount ranging from 1 to 99% byweight of the composition.
 7. A composition according to claim 1 whereinthe oily base is present in an amount ranging from 50 to 99% by weightof the composition.
 8. A composition according to claim 1, wherein theoily base is present in an amount ranging from 80-99% by weight of thecomposition.
 9. A composition according to claim 1 wherein thermoplasticelastomer is a thermoplastic rubber.
 10. A composition according toclaim 1 wherein the thermoplastic elastomer is present in an amount inthe range of 1-10% by weight of the composition.
 11. A compositionaccording to claim 1, wherein the thermoplastic elastomer is present inan amount ranging from 2-9% by weight of the composition.
 12. Acomposition according to claim 1, wherein the thermoplastic elastomer ispresent in an amount ranging from 3-8% by weight of the composition. 13.A composition according to claim 1 containing one or more anti-oxidants.14. A cable containing a cable filling or cable flooding compositioncomprising a dispersion of hollow expanded micro spheres in a gelcomposition comprising an oily base and a thermoplastic elastomer,wherein the micro spheres each have a shell formed of a copolymer ofacrylonitrile and methacrylonitrile, said copolymer having CAS RegistryNo. 38742-70-0.
 15. A cable according to claim 14 comprising aconducting core surrounded by a sheath, wherein said composition isdisposed between the conducting core and the sheath.
 16. A cableaccording to claim 15, wherein the conducting core is an electricalconductor or a light conductor.